Texas Instruments ADS7042EVM-PDK, User Manual

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1
3
2
4
8
OPA2320AIDGKR
U10A
7
5
6
4
8
OPA2320AIDGKR
U10B
AGND
100nF
C25
OPA_VDD
OPA_VDD
0
R45
DNP
AGND
AVDD/4
VBIAS
AINM
AVDD/2
Figure 2-6. Buffer Amplifier Circuit on the ADS704X-5XEVM
The buffer amplifier in Figure 2-6 prevents the AVDD/4 resistor divider (R3 and R5) from loading the amplifier
inputs and the AVDD/2 resistor divider (R7 and R9) from loading the ADC inputs (see Figure 2-4 ). As per Section
2.1.1 , VBIAS sets the driver amplifier common-mode voltage for both signal paths. AINM is only required if U3 or
U5 in Figure 2-2 is populated with the ADS7043. This specific ADC has a pseudo-differential input that requires
the AINM pin to be set to AVDD / 2 ±100 mV.
When the ADS7043 is used on the ADS704X-5XEVM:
• Populate R39 in Figure 2-4 with a 0-Ω resistor
• Populate R45 in Figure 2-6 with a 0-Ω resistor
• Depopulate R40 in Figure 2-2
2.3 Digital Interface and Communication
The EVM interfaces with the PHI and communicates with the computer over the USB. There are three devices
on the EVM with which the PHI communicates: the two ADCs (over SPI) and the EEPROM (over I
2
C). The
EEPROM comes preprogrammed with the information required to configure and initialize each ADC populated
by default on the ADS704X-5XEVM. Therefore, communication with the EEPROM is only required if the user
removes and replaces one of the default ADCs. See
Section 2.4 for more information.
All ADCs supported by the ADS704X-5XEVM use SPI serial communication in mode 1 (CPOL = 0, CPHA
= 1). The ADS704X-5XEVM offers 49.9-Ω resistors between the SPI signals to aid with signal integrity (see
Figure 2-2 ) because the serial clock (SCLK) frequency can be as fast as 60 MHz. Typically, in high-speed SPI
communication, fast signal edges can cause overshoot; these 49.9-Ω resistors slow down the signal edges to
minimize signal overshoot. JP5 provides test points to measure the digital signals, as illustrated in
Figure 2-7 .
Introduction to the ADS704X-5XEVM www.ti.com
8 ADS7042EVM-PDK, ADS7049-Q1EVM-PDK, and ADS7057EVM-PDK
Evaluation Module SBAU382 – NOVEMBER 2021
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